The present invention is related to electro-pneumatic brake systems for railroad freight cars and particularly to a pneumatic backup brake control for the electrically controlled electro-pneumatic brake system.
Electro-pneumatic brake systems have been proposed for railroad freight cars which, when coupled in a train of such cars, will achieve a more uniform braking action throughout the train due to the near-instantaneous brake response at each car.
For purposes of convenience and cost effectiveness, it has been proposed to employ the existing freight brake control valve device for the pneumatic backup control, with the electro-pneumatic and pneumatic systems being separated by a double check valve device. Brake pipe pressure effective at each car normally remains charged to hold the freight brake control valve in its release position in a manner well-known to those in the railroad related industries. When a brake application is called for, the electro-pneumatic brake control system operates via the double check valve to control the brake pressure supplied to the car brake cylinder devices. In the event this pressure fails to develop, due to loss of electric power in the event of a train break-in-two, for example, brake pipe pressure would be concurrently depleted and the pneumatic backup brake control valve accordingly operated in response to such reduction of brake pipe pressure to apply brake pressure via the double check valve. While the pneumatic brake control valve is capable of applying brake pressure in graduated amounts dependent upon the degree of brake pipe pressure reduction, it will be appreciated that in a backup role, as herein proposed, the control valve is only required to apply full brake pressure.